The present invention relates to an electrical synchronous machine, in particular for use as a drive unit in motor vehicle applications, comprising a stator which has an electrical winding arrangement for generating a rotating field, and comprising a rotor which has magnetic flux generating means for generating a rotor flux with which the rotating field interacts.
In conventional synchronous machines, the rotor flux is generated by poles which are magnetized by DC coils. In this case, the field current is generally transmitted to the rotor via slip rings.
In conventional synchronous machines, the rotating field generated by the stator winding is generated by means of the three phases of rotating current.
However, the rotor flux can also be generated by permanent magnets. A synchronous machine of this type can be constructed without slip rings. In this case, power is supplied to the stator winding generally from control and power electronics which, for example, are supplied with power from a DC voltage supply system (for example an electrical vehicle supply system). Machines of this type are also called electronically commutated DC machines or EC motors. These motors can have a long service life, are generally maintenance-free and can be designed for a high degree of protection. Stepless rotation speed control is generally possible by means of the electronic control system.
Synchronous machines are generally designed for a specific rated rotation speed. The rotor flux generated by the magnetic flux generating means is reduced by electrical field weakening at rotation speeds greater than the rated rotation speed.
Permanent magnet-excited synchronous machines are generally designed for a high torque. In this case, the rotor flux is generally comparatively high. As an alternative, such machines can also be designed for a high rotation speed, the rotor flux then generally being lower.
However, on account of the constant rotor flux, the system is generally fixed to a specific rated operating point. In the case of rotation speeds rising beyond this, electrical field weakening is so great that only a relatively small portion of the power fed to the winding arrangement of the stator is available as drive power. Therefore, a range of very high rotation speeds can generally no longer be used. This is true particularly in the case of synchronous machines in which a high rotor flux is generated by correspondingly designed magnetic flux generating means (for example permanent magnets). If generation of higher rotation speeds, in particular a larger usable rotation speed range, is desired, this can generally be realized only with a lower rotor flux. However, this results in the maximum torque being reduced.
DE 36 09 835 A1 discloses a single-phase motor with a permanent magnet rotor and an electromagnetically excited stator, the rotor having two permanent magnet disks which are seated on the rotor shaft in a rotationally fixed manner at an axial distance from one another and have magnetization directions which are oriented transverse to the rotor axis and parallel to one another.
DE 34 20 370 C2 discloses a further single-phase motor with a two-part rotor which has a permanent magnet rotor inner part which is mounted on a drive shaft in a freely rotating manner, and an electrically conductive rotor outer part.
Document DE 33 23 297 C2 discloses an induction motor with low inertia, a yoke which is rotatably mounted in a frame of the stator and is provided with fan blades being arranged between the stator and rotor.